Pourable aqueous blasting composition

ABSTRACT

A water resistant, stable, pourable, aqueous blasting composition is provided which employes as its thickening system a combination of a non-cross-linked thickening agent and a small amount of a self-complexing thickening agent. The composition is pourable from a package into receptacles as small as three inches in diameter or less.

United States Patent 1 1 1 3,925,123 Jessop Dec. 9, 1975 [5 POURABLEAQUEOUS BLASTING 3,658,607 4/1912 Cook et a1. [49/44 x COMPOSITIONHarvey A. Jessop, Murray, Utah IRECO Chemicals, Salt Lake City, UtahFiled: Oct. 11, 1974 App1. No.: 514,205

Inventor:

Assignee:

US. Cl. 149/60; 149/41; 149/42; 149/43; 149/44; 149/60; 149/61; 149/70;149/76; 149/83; 149/85 Int. Cl. C0613 31/30 Field of Search 149/44, 41,60, 42, 76. 149/43, 61, 70, 83, 85

References Cited UNITED STATES PATENTS 11/1971 Craig et a1. 149/44Primary Examiner-Stephen J. Leche rt, Jr. Attorney, Agent, or FirmRobertA. Bingham [57] ABSTRACT A water resistant, stable, pourable, aqueousblasting composition is provided which employes as its thickening systema combination of a non-cross-Iinked thickening agent and a small amountof a selfcomplexing thickening agent. The composition is pourable from apackage into receptacles as small as three inches in diameter or less.

4 Claims, No Drawings POURABLE AQUEOUS BLASTING COMPOSITION The presentinvention relates to an aqueous explosive blasting composition ofimproved pourability. More particularly, the present invention relatesto an aqueous explosive blasting composition having a continuous liquidphase, wherein the phase has a fudge point below intended temperaturesof use and comprises an aqueous solution of inorganic oxidizer salt orsalts containing a thickening system comprising a combination of anon-cross-linked thickening agent and a small amount of aself-complexing thickening agent. This thickening system renders thecomposition pourable into receptacles as small as three inches indiameter or less while simultaneously rendering it stable and waterresistant. Moreover, this thickening system reduces tackiness andimparts stringiness to the composition such that the composition doesnot unduly adhere to a package or lose its integrity during pouring.

As used herein, the phrase as small as three inches in diameter or lessmeans the composition must be pourable into a receptacle at least assmall as three inches in diameter. According to the present invention,it is possible, however, to prepare effective blasting compositionswhich are pourable into diameters as small as one-inch or even one-halfinch as a practical lower limit.

BACKGROUND Blasting agents of the type commonly known as wa ter-bearing,aqueous or slurry explosive blasting compositions have come intoprominent use in recent years. Blasting agents of this type generallycomprise a viscous, continuous fluid phase throughout which solidingredients and gas bubbles may be dispersed, For example, such an agentmay comprise an aqueous solution of inorganic oxidizer salts forming thecontinuous phase of the agent; solid ingredients dispersed throughoutthe solution such as undissolved oxidizer salts or particulate fuelssuch as aluminum, carbinaceous materials, sulfur, etc.; organic liquidfuels of either a watermiscible or immiscible nature such as alcohols,glycols, amides and analogous nitrogencontaining liquids generallyhaving good solvent properties for the oxidizer salts and liquidhydrocarbons such as benzene, toluene, fuel oil, etc., respectively;thickening and cross-linking agents and, if desired, numerous, tiny,finely dispersed gas bubbles or microballoons.

Aqueous blasting agents or compositions are usually thickened and thusrendered viscous by the inclusion of hydratable thickeners such as guargum, starch, flour, etc. Thickening is important for maintaining thehomogeneity and integrity and thus stability of a composition. Forinstance, compositions often contain numerous, finely dispersed gasbubbles which are produced either mechanically by entrainment duringformulation or chemically by decomposition of a gassing agent which isincluded in the composition. Tiny, well-dispersed gas bubbles greatlycontribute to a compositions sensitivity to detonation, and properthickening inhibits bubble migration and coalescence which would reducethis sensitivity. Similarly, thickening inhibits finely divided anddispersed particulate fuel ingredients from gravitationally segregatingin the composition. This segregation could reduce the compositionssensitivity and detonating ability. Thus proper thickening is extremelyimportant with regard to composition stability.

A compositions stability can be and frequently is further enhanced bythe inclusion of cross-linkers which cross-link the molecules of thethickening agent together thereby forming a chained molecular networkwhich imparts a desired degree of firmness or rigidity to thecomposition. Thus, in addition to thickening, proper cross-linking canfurther enhance water resistance and further inhibit constituentmigration, segregation and coalescence.

For use in adverse environments such as water-containing boreholes orhigh-temperature boreholes where degradation of thickening agents mayoccur, relatively higher amounts of thickening agents are generallyemployed. In such situations, the thickening agents are usuallycross-linked for added stability.

One of the main advantages of aqueous blasting compositions is that theycan be used in the presence of water provided they are properlythickened (and preferably cross-linked) so that breakup of thecomposition and leaching of the soluble oxidizer salts is prevented.These compositions can be formulated and pumped without protectivepackaging directly into water-containing boreholes. U.S. Pat. No.3,303,738 discloses a method by which on-site formulation and pumping ofa composition into a borehole is accomplished. For use in watercontaining boreholes, such compositions have obvious advantages overnon-slurry, non-water-resistant compositions such as ANFO which requirewaterproof packaging.

Recently, aqueous blasting agents have been packaged in stick-like formand used as a replacement for stick dynamite. For example, US Pat. No.3,878,254 describes compositions adaptable for packaging, and U.S.. Pat.No. 3,783,735 discloses an apparatus for preparing and packaging suchcompositions in stick form. These packaged slurry explosives aregenerally used in boreholes too small in diameter for filling by directpumping. Even when packaged, however, these explosives are generallysufficiently thickened for good water resistance in case the packagebecomes ruptured in a water-containing borehole. Such thickening is alsoimportant for the overall stability of the explosive. Normally, thesepackaged explosives are highly thickened and cross-linked and thus arein the form of a firm gel.

It is oftentimes desirable, and it is the object of the presentinvention, to have a packaged slurry explosive that can be poured fromits package or container into a borehole or receptacle of desireddiameter and shape. This packaged blasting agent can be convenientlystored and transported in packages of desired size and then poured intothe receptacle or borehole for use. Packaged slurry adaptable for thisuse will be hereafter referred to as a pourable slurry or pourableblasting agent.

A pourable slurry must be fluid enough for pouring, but at the sametime, be sufficiently thickened and cross-linked to be water resistantand stable. Thus the viscosity of the composition must be compromised inorder to accomodate both pourability and water resistance and stabilityrequirements. Additionally, since aqueous blasting agents in generaltend to be tacky, particularly those which are readily flowable, andthus tend to adhere to the inside of a package when poured, and sincemany such agents would tend to break apart and lose their integrityduring pouring due in part to their adhesion to the package; it isimportant that the 3 pourable slurry not have undue tackiness and havesufficient stringiness in order that it will maintain its integrity whenpoured from the package. Stringiness prevents the slurry from tearingapart and also helps the slurry to pull itselfout of the package when itis poured.

Thus the important characteristics of a pourable aqueous blasting agent,vis-a-vis aqueous blasting agents in general, are their thickening andcross-linking characteristics with regard to pourability, waterresistancy, tackiness. and stringiness.

It has been found that a thickening system compris ing a combination ofa non-cross-linked thickening agent and a small amount of aself-complexing thickening agent is capable of providing a pourableslurry which is water resistant, stable and concomitantly pourable intoreceptacles three inches in diameter or lessv SUMMARY OF THE INVENTIONThe present invention comprises a water-resistant, thickened, aqueous,inorganic oxidizer salt-containing, fueled, explosive composition orblasting agent having a continuous liquid phase with a fudge point belowintended temperatures of use and containing a thickening systemcomprising a combination of a non-cross-linked thickening agent and asmall amount ofa self-complexing thickening agent, which combinationrenders the composition pourable into receptacles as small as threeinches in diameter or less while simultaneously rendering thecomposition stable and water resistant.

DESCRIPTION OF PREFERRED EMBODIMENT The compositions of the presentinvention contain inorganic oxidizer salts dissolved in an aqueous fluidphase. The oxidizer salts are selected from the group which consists ofammonium, alkali and alkaline earth metal nitrates and perchlorates,e.g., sodium, calcium and ammonium nitrates and perchlorates. isessential that substantially all of the oxidizer salt remain in solutionat intended temperatures of use of the composition, and, therefore,eutectic combinations of the salts are normally preferred. Thus two ormore salts are generally present in the solution, for example, ammoniumnitrate (AN) and sodium nitrate (SN) or AN, calcium nitrate (CN) and SNcombinations. Although the total amount of salt which can be employed inthe compositions and which will remain in solution at intendedtmeperatures of use (generally down to at least 5C) can varysubstantially depending upon the total amount of water and amount andtype miscible organic liquid used, if any, as well as the particularproportions and combinations of oxidizer salts themselves; generallyfrom about 40 to about 70% by weight, based on the total composition, oftotal oxidizer salts are employed in the compositions of the presentinvention. The examples given below illustrate several representativeamounts and combinations of salts.

Water is an essential ingredient in the compositions since it functionsas at least part of the solvent for the oxidizer salts and, by helpingto maintain the salts completely in solution, provides sufficientfluidity to a composition to render it pourable. The amount of waterrequired for complete dissolution of the salts in the aqueous solutionat intended temperatures of use depends upon that temperature and thevarious factors listed above and is easily determinable by one skilledin the art. Water is normally present in compositions of the presentinvention in amounts of from about 10 to about 40% by weight, andpreferably greater than 20%.

It is usually desirable, although not essential, that a watermiscibleorganic liquid fuel be employed both as a fuel and as an additionalsolvent for the oxidizer salts. Because an organic liquid functions asan extender for water, in addition to its function as a fuel, itsinclusion can generally increase the detonation energy of thecomposition since it can replace part of the water which in high amountsis detrimental to energy production. Typical water-miscible organicliquid fuels are well known in the art and include alcohols, glycols,amides and analogous nitrogen-containing liquids. Several representativeliquids are illustrated in the examples below. Such liquids aregenerally employed in amounts varying from 0 to about 20% by weight.

Although not essential, solid, particulate fuel ingredients common tothe art are usually incorporated into the compositions of the presentinvention. These ingredients are normally added in amounts sufficient orin excess of that required to provide substantially an oxygen-balancedcomposition. For example, finely divided aluminum particles may bepresent in amounts of up to 40% by weight or more, although they wouldusually be present in lower amounts. They should be in finely dividedform so as not to unduly interfere with the required fluidity orpourability of the composition.

The thickening system is the important concept of the present inventionand comprises a combination ofa non-cross-linked thickening agent and asmall amount of a self-complexing thickening agent. This combinationrenders the composition pourable into receptacles three inches indiameter or less while simultaneously rendering it stable and waterresistant.

The non-cross-linked thickening agent provides sufficient thickening togreatly contribute to overall stability and water resistance, but, sinceit is not cross-linked, the composition remains pourable. An appropriatethickening agent or combination of non-cross-linked thickening agentsmay also impart high temperature (60) stability to the composition.Typical non-crosslinked thickeners are well known in the art and includeflours, starches, polysaccaride polymers such as guar gum, and syntheticpolymers such as polyacrylamides or biopolymers. These thickening agentsalso perform the essential functions of holding in place finelydispersed, sensitizing gas bubbles and preventing substantialsegregation of dispersed, particulate ingredients. It is essential thatsufficient non-cross-linked thickening agent is present to perform thesefunctions, and it is essential that it not be cross-linked in order thatthe composition can remain pourable. Although the amount ofnon-cross-linked thickening agent required depends upon the desiredphysical characteristics and nature of the composition as determined byits ingredients and the type of thickening agent employed, generallyfrom about 0.2 to about 6% by weight and preferably from about 1 toabout 3% is employed.

A self-complexing thickening agent (generally a gum) is an essentialingredient of the invention since it is primarily responsible forimparting stringiness to the composition, and it also reduces tackinesswhich rende rs the composition more easily pourable from a package. Aminimum but limited degree of cross-linking is required for adequatestringiness and generally for good stability, and a self-complexing gumprovides such cross-linking in an easily controllable amount.Self-complexing or self-cross-linking" gum contains its own cross-linkerwhich comes into effect when the gum is hydrated in solution. These gumsare known in the art and typically include a powdered mixture of guargum and cross-linker. Antimony, borate and chromate cross-linkers aretypically used. A preferred selfcomplcxing gum is Stein-Hall EX-23."Other gums from the series can be used. General Mills also manufacturesmany self-complexing gums. The self complexing thickening agent isgenerally present in an amount of from about 0.l to about 0.5% by weightand preferably from about 0.l to about 0.3%.

The inclusion of a self-complexing thickening agent reduces the totalamount of thickeners required since it provides a limited but anecessary threshold amount of cross-linking. lt is extremely difficultby conventional means to control reliably the degree of cross-linking ofan aqueous blasting agent where that degree must necessarily bemaintained at a very small amount in order for the composition to bepourable. Thus it is difficult if not practicably impossible to addcross-linker to a thickened solution as a separate ingredient andattempt to limit the degree of cross-linking to a very small amount inorder for a composition to remain pourable. However, if most of thethickening agent is non-crosslinked. and the small amount ofcross-linking that is required can be provided by selectivelycross-linking only a small portion of total thickening agent, reliablecontrol becomes feasible. This control is accomplished by the use of aself-complexing gum which is selectively cross-linked by its ownself-contained cross-linker. Thus cross-linker need not be separatelyadded to a composition, and an accurate means of reliably controllingthe degree of cross-linking of the composition is accomplished byvarying as desired the amount of self-complexing thickening agent added.

The invention can be better understood by reference to the examplesgiven below.

EXAMPLE 1 A composition of the present invention (and compositions ofthe present invention in general) was (can be) prepared in the followingmanner: the oxidizer salts were dissolved in water to form a solutionhaving a fudge point of approximately 0C. The solution was heated toabout C or C and then the watermiscible liquid fuel and guar gum wereadded. The resulting solution mixture was allowed to thicken and wasthen mixed to homogeneity with the remaining ingredients including theself-complexing gum and starch thickeners. Mixing and pumping wasaccomplished by conventional means. This blasting agent had thefollowing composition (percentages are by weight):

Sclf-complcxing (lum (EX-23] The solution of this composition had afudge point of 2C. At 30C. the solution had a viscosity of 800 to l200centipoiscs. It has a pH of 4.0 i 0.2 and a density of 1.33 g/cm at 30C.At 5C. the composition had a critical diameter (the minimum chargediameter for successful propagation of a detonation wave) of from 2 to 2A inches at a density of 1.2] g/cm.

The composition of this example is water resistant and is pourable froma polyethylene package having a diameter of five inches into a threeinch diameter borehole or other receptacle.

The thickening system of this example, comprising non-crosslinked guargum, non-cross-linked starch, and self-complexing gum, is particularlyeffective. This combination provides concomitantly high temperature (upto 60C) stability and low temperature (down to 5C) pourability. Thestarch provides thickening which is stable at high temperatures; thenon-cross-linked gum provides good overall thickening of the liquidphase without adversely affecting pourability; and the self-complexinggum reduces tackiness and imparts stringiness which enhances integrityduring pouring and addes to overall water resistance.

EXAMPLE 2 Other compositions were prepared in the manner described aboveand have the fonnulations, properties and etonation results indicated inTable 1 below. All of these compositions are water resistant and capableof being effectively poured from a container such as a polyethylene baginto a receptacle as small as three inches in diameter or less. Thecompositions are not unduly tacky and have good stringiness and thusmaintain their integrity during pouring.

The compositions of the present invention can be packaged byconventional means in a container or package of essentially any desiredsize and shape. They are preferably packaged in an elongated orcylindrical polyethylene bag having an average cross-sectional diameterof about five to about seven inches. The packaged composition generallyhas a safe, reliable storage life of up to about one year or more underreasonable storage conditions. When the packaged explosive is to beused, the package is opened or cut, usually at one end, and thecomposition poured" out of the package and into a desired receptacle.Even though the composition is pourable from a package, it isnevertheless sufficiently thickened and has at least a minimum degree ofcross-linking (having a viscosity of generally about 15,000 to about75,000 centipoises) to be water resistant and stable and thus can bepoured into water-containing receptacles or boreholes and can bedetonated even after remaining in a water-containing borehole for manydays. At l5,000 centipoise, compositions of the type shown in the aboveexamples are pourable into two inch diameter receptacles. At 75,000centipoises, the compositions are still pourable into 2% to 3 diameterreceptacles.

While the present invention has been described with reference to certainillustrative examples and preferred embodiments, various modificationswill be apparent to those skilled in the art and any such modificationsare intended to be within the scope of the invention as set forth in theappended claims.

TABLE I Composition C Ingredients (parts by weight) AN 38 22 25 I lip sercilia What is claimed is:

1. In a water resistant explosive composition which contains an aqueousinorganic oxidizer salt solution forming a continuous fluid phasethroughout the eomposition and having a fudge point below intendedtemperatures of use of the composition; the improvement comprising athickening system consisting essentially of a combination ofnon-cross-linked guar gum and starch and a small amount of aself-complexing thickening agent, which thickening system simultaneouslyprovides water resistance, stability at temperatures as high as 60 C andpourability into receptacles as small as 3 inches in diameter or less attemperatures as low as 5 C 2. A composition as defined by claim 1wherein water is present in an amount of about 10 to about 40% byweight.

3. A composition as defined by claim 1 comprising about .2 to 3% byweight guar gum, about 0.5 to 2% starch and about 0.05 to about 0.25% ofthe self-complexing gum.

4. A composition as defined by claim 3 comprising about 40 to by weightof an inorganic oxidizer salt selected from the group consisting ofammonium, alkali and alkaline earth metal nitrates and perchlorates andmixtures thereof; about 10 to 40% water; from about 0 to about 20% of awater-miscible organic liquid fuel and from 0 to about 40% ofparticulate fuel.

1. IN A WATER RESISTANT EXPLOSIVE COMPOSITION WHICH CONTAINS AN AQUEOUSINORGANIC OXIDIZER SALT SOLUTION FORMING A CONTINUOUS FLUID PHASETHROUGHOUT THE COMPOSITION AND HAVING A FUDGE POINT BELOW INTENDEDTEMPERATURES OF USE OF THE COMPOSITION; THE IMPROVEMENT COMPRISING ATHICKENING SYSTEM CONSISTING ESSENTIALLY OF A COMBINATION OFNON-CROSS-LINKED GUAR GUM AND STARCH AND A SMALL AMOUNT OF ASELF-COMPLEXING THICKENING ASENT, WHICH THICKENING SYSTEM SIMULTANEOUSLYPROVIDES WATER RESISTANCE, STABILITY AT TEMPERATURES AS HIGH AS 60*C ANDPOURABILITY INTO RECEPTACLES AS SMALL AS 3 INCHES IN DIAMETER OR LESS ATTEMPERATURES AS LOW AS 5*C.
 2. A composition as defined by claim 1wherein water is present in an amount of about 10 to about 40% byweight.
 3. A composition as defined by claim 1 comprising about .2 to 3%by weight guar gum, about 0.5 to 2% starch and about 0.05 to about 0.25%of the self-complexing gum.
 4. A composition as defined by claim 3comprising about 40 to 70% by weight of an inorgaNic oxidizer saltselected from the group consisting of ammonium, alkali and alkalineearth metal nitrates and perchlorates and mixtures thereof; about 10 to40% water; from about 0 to about 20% of a water-miscible organic liquidfuel and from 0 to about 40% of particulate fuel.